|
Mating
When it's springtime in the
Rockies, grizzly bears begin their mating rituals. The whole mating
process starts in mid-May to mid-June. From afar, scientists have watched
grizzly bear courtship and copulation in the wild. They believe that in
springtime, females leave scent trails for wandering males to follow. Such
trails may be the key to finding a female bear in areas where grizzly
populations are at very low densities. Such is the case in the Central
Rockies Ecosystem where there is only 1 bear for every 50 to 100 sq. km.
When a male finds a female, the process of getting to know one another
begins. At any other time of the year, grizzly bears are solitary
creatures that will avoid close encounters with other bears, especially
large adult males. During mating season, however, solitary bears let down
their guard a little although not for long.
Not surprisingly, male and
female grizzly bears usually spend at least a few days testing one another
before mating occurs. This type of interaction is important when getting
to know an animal that is strong enough to injure or even kill you. The
two bears may chase each other, play fight or even nuzzle and lick each
other once they are aquainted. The outcome of this process may be
rejection or the formation of a pair bond that lasts from several days to
a couple of weeks.
In Banff and Waterton Lakes
National Parks, researchers have observed an amazing mating ritual. Male
grizzly bears have been seen "herding" females onto mountain
tops. In doing so, a male is able to isolate a female so that her scent
does not attract other bears. In Banff National Park, a male bear kept a
female confined within a 2 to 3 hectare mating area for 13 days. On
occasion, the female bear tried to escape but the persistent male cut her
off and sent her back up the ridge.
At first, a male's approaches
are rejected by the female with paw swats, charges or bites. Eventually,
repeated copulation occurs over a few days. The adult male is 1.5-2.0
times larger than the female and mounts her from the rear. At first,
copulation may last a few minutes but there may be several bouts that last
up to one hour.
Shortly after these prolonged
copulations, the male and female separate. The female will likely become
pregnant but this does not necessarily mean she will have cubs the
following spring. Grizzly bears have developed a process called delayed
implantation. At first, the embryo floats freely in the female bear’s
uterus and its development is delayed. Sometime in the fall, the female's
body senses whether she will be able to store enough fat reserves to
support herself and her cub over the winter. If she can, the embryo is
implanted in the uterine wall and it begins to grow. If her energy stores
are low, the embryo is reabsorbed by her body and she will not give birth
to cubs the following spring.
After mating, the male
grizzly bear has no further association with the female. The female may
mate with other males but the period of reproductive readiness is brief.
If she does mate again, and her fat stores are adequate, she may even give
birth to several cubs from different fathers. This explains why cubs from
the same litter can look very different from one another. In about 1.5 to
4.5 years, the cubs will leave their mother’s side. At this time the
female grizzly bear is free to embark on the whole mating ritual again.
Suggested specific readings:
Herrero, Stephen, and David
Hamer. 1977. Courtship and copulation of a pair of grizzly bears, with
comments on reproductive plasticity and strategy. J. Mammal. 58(3):
441-444.
Hamer, David, and Stephen
Herrero. 1990. Courtship and use of mating areas by grizzly bears in
the Front Ranges of Banff National Park, Alberta. Can. J. Zool.
68(12): 2695-2697.
|
IN ESPAÑOL!
IN DEUTSCH!
IN ENGLISH!
